Hepatocyte Growth Factor (HGF) is a heparin binding protein that stimulates proliferation, migration and morphological differentiation of a variety of cellular targets. This signaling is important for normal development of liver, placenta, neural development, and contributes to cytoprotection and repair in the kidney, liver and lung tissues. Our interest has focused on the Hepatocyte Growth Factor and its interaction with MET. Heparin binding to HGF has been implicated in ligand-induced dimerization of the Met receptor. We determined that the primary binding site for such heparin oligosaccharides resides in the N-domainn of NK1. The structure of NK1 has been determined previously by our group and others;however, the nature of the heparin interaction and dimerization remains unclear. We are completing a solution structure of monomeric NK1 that indicates a conformational rearrangement is required to shift from the free protein to that seen in crystals and bound to heparin. A panel of heparin-binding mutants of NK1 were developed and tested for antagonistic activity. The mutants were found to yield a potent and selective competitive antagonist of oncogenic HGF signaling in vivo. A manuscript describing this work was not accepted by Science, and additional experiments have been conducted for submission to Cancer Cell. The structural work on NK1 is expected to conclude in FY2010.